1. Field of the Invention
The present invention relates to a battery charger or booster and in particular to a high frequency charger.
2. Technical Background
Dual-mode battery chargers currently exist. When operated in a first mode, the battery charger delivers a high current output for a short duration of time. This short duration, high current can be used to jump-start a vehicle with a dead battery. In a second mode, the battery charger provides a low current output that is used to charge the battery back to its full charge. Known dual-mode battery chargers typically use a single large transformer to achieve the dual-mode capability. The single transformer is usually a linear type transformer. A tap of a primary winding of the transformer is changed in order to achieve the dual capability with the linear-type transformer. As the tap of the transformer is changed, the output voltage, and hence, according to Ohm's Law, the output current of the transformer is changed, resulting in the dual-mode capability. Use of a single transformer for both modes of operation has the advantage of being very cost-efficient and very effective.
However, this approach also has several disadvantages. One of the disadvantages is that known single transformer battery chargers are very large and cumbersome. Standard linear transformers require iron for their cores, adding to the weight of the battery charger. They also require orders of magnitude more wire to form their windings than do high frequency chargers, again adding to the weight of the battery charger.
Additionally, although the linear transformer can provide a high current output, the high current output can only be provided for a very short period of time. As the transformer operates in high current mode, it generates an excessive amount of heat. In fact, so much heat may be generated that the transformer actually melts down. If a meltdown occurs, the transformer will not operate in either the high current mode or the low current mode. Linear transformers are also very lossy in terms of magnetic losses and eddy current losses, resulting in inefficiency.
Further, to charge an automobile battery that is of insufficient electric power by providing power from another power source, like a battery charger, the power source and the battery must be connected through a pair of electric wires, typically having clamps at their ends for connection to the battery. Making this connection can be very dangerous if there is a problem with the connection. For example, it is well known that sparking or arcing often occurs when a connection is being attempted between a battery charger and a battery. Additionally, sparking or arcing may occur when the clamps are connected to the battery with a reverse polarity. Sparking or arcing can also occur even after an apparently good connection is made. The sparking or arcing may occur due to corroded or poor terminal connections.
In the past, the use of a delay circuit or “soft start” was used to prevent sparking. A delay circuit prevents power flow to the battery from occurring until a connection is made between the battery and the battery charger. This method helps to prevent sparking upon the initial connection of the battery and battery charger. However, it does not prevent any sparking that occurs as a result of poor or corroded connections, the existence of which can only be determined after current flow begins. Sparking or arcing may result in damage to the battery, and under certain circumstances, an explosion, fire and damage to the vehicle or to a person may result.
Additionally, a characteristic of liquid electrolyte type batteries, particularly lead acid batteries used in vehicles, is that chemical compound deposits slowly build up on the plates to partially or entirely cover and displace the normal plate surfaces. Low current recharging is inadequate in that it can not, as such, sufficiently remove such deposits that with the passage of time crystallize and choke the battery plates by interfering with electrolyte movement. When this occurs a battery may still appear to have taken a charge and even the electrolyte may check as being correct, but the battery does not hold the charge because the plates are effectively shorted. Batteries using other electrolytes also face reclaiming, maintenance and charging problems that need to be successfully addressed.
Thus, there is a need for a method to release the deposits that are built up on the plate surfaces, where the deposits may either go back into the solution or be broken up. There is also a need for a simple and lightweight dual-mode battery charger. The battery charger should be able to provide a high current output that is sufficient to start an automobile or other vehicle with a dead battery, yet be easy to construct and safe to operate.